1. Field of the Invention
This invention relates in general to the performance monitoring of communication systems, and more particularly to a method and apparatus for measuring a change in the insertion loss of a transmission line in a communication system.
2. Description of Related Art
Cellular communication systems are experiencing tremendous growth in the global communication market place. This growth is fueling many research programs and expanding the technology opportunities for all manufacturers of cellular equipment.
To attract customers and obtain a larger market share, cellular providers are pushing features enabled by the system's purely digital nature, such as Caller ID and short messaging, a paging equivalent. To further obtain a larger market share, cellular providers have turned to reducing the cost of air time. Cutting prices can take many forms. For example, vendors can give more free minutes per month, charge less for additional minutes, charge nothing for the first minute of incoming calls, reduce monthly fees, eliminate long-term contracts—all tactics available to the established cellular vendors as well. For a provider, this leads to less revenue per customer, but more incentive for increasing the market share. Thus, any reduction in customer traffic due to network problems has a tremendous impact on revenues and profits.
Accordingly, cellular vendors must take every step to ensure the reliability of the cellular network to maximize customer traffic. One problem encountered by cellular operators is an increase in the measurable loss (S21) of the feeder coax cable. The symptoms of loss via a deteriorated S21 typically involves a reduction in Base Transceiver Station (BTS) traffic, an increase in the number of dropped calls and an increase in subscriber complaints.
Typical causes for an increase in feeder cable loss include water in the feeder cable, mechanical stress placed on the cable during instillation, temperature cycling of the cable, connector failure and the effects of UV light on the cable. To make matters worse this type of problem occurs gradually. This makes the detection of this problem much more difficult.
Current systems and methods for monitoring the performance of feeder cables involve the measurement of the reflected RF power from the transmitter at the frequency of the BTS operation. However, this method allows only for the detection of an impedance change in the cable (S11 ) i.e. if the cable is no longer presented 50Ω to the BTS output connector or not. Current systems and methods for monitoring the performance of feeder cables do not directly measure the insertion loss of the feeder cable (S21). Still, an increase in the insertion loss of a feeder cable may occur with no or very little change in the cables impedance, and therefore no indication of a change in the performance of the feeder cable will be detected by current systems and methods for measuring the performance of feeder cables.
It can be seen then that there is a need for a method and apparatus for detecting the presence of a deterioration in the cable insertion loss.